(i) Field of the Invention
The present invention relates to an improved electrophotographic photoreceptor for use in various printing machines and copying machines.
(ii) Description of the Related Art
In general, there are various electrophotographic processes, and typical known examples thereof include a direct process and a latent image transfer process. In each electrophotographic process, an electrophotographic photoreceptor is used, and this electrophotographic photoreceptor contains a photoconductive layer which is made from a photoconductive material. Here, the photoconductive material should possess following fundamental characteristics:
(1) that a high charging potential is generated by corona discharge in the dark, PA1 (2) that the electric charges generated by the corona discharge scarcely attenuate in the dark, PA1 (3) that the electric charges are eliminated promptly by light irradiation, PA1 (4) that less electric charges remain after the light irradiation, PA1 (5) that a residual potential is scarcely increased and an initial potential is scarcely decreased, even when repeatedly used, and PA1 (6) that electrophotographic properties scarcely change by temperature and humidity. PA1 (1) compatibility to a binder being low, PA1 (2) crystals being easily deposited, PA1 (3) sensitivity change being liable to occur, when repeatedly used, PA1 (4) charging properties and repeating properties being poor, and PA1 (5) residual potential properties being poor. PA1 a conductive support; and PA1 a photosensitive layer formed on the conductive support, the photosensitive layer containing an enamine derivative as a carrier transport material represented by the formula (I) ##STR2## wherein Ar is an aryl group which may have a substituent, a heterocyclic group which may have a substituent, an aralkyl group which may have a substituent, or a heterocyclic substituted alkyl group; and n is 2, 3 or 4 .
As materials which can meet the above-mentioned requirements, there have been used inorganic photoconductive materials such as zinc oxide Japanese Patent Publication No. (Sho) 57-19780!, cadmium sulfide Japanese Patent Publication No. (Sho) 58-46018! and amorphous selenium alloys, but in recent years, various problems are taken up. That is to say, when the zinc oxide material is used, the addition of a sensitizer is necessary to increase a sensitization effect, but owing to the presence of the sensitizer, the charging by the corona discharge declines and decoloration tend to occur by exposure. In consequence, a stable image cannot be kept up for a long period of time. With regard to the cadmium sulfide material, a stable sensitivity cannot be obtained under the conditions of a high humidity. The selenium material has some drawbacks such as the easy advancement of crystallization due to external factors such as temperature and humidity, the deterioration of charging properties, the occurrence of white dots on an image, the difficulty of manufacture and strong toxicity.
In view of future views, researches have been actively conducted on electrophotographic photoreceptors made of organic materials instead of inorganic materials which have problems such as exhaustion of resources, toxicity and environmental pollution. As a result, the electrophotographic photoreceptors using various kinds of organic compounds have been developed. Among others, according to the researches and developments in the last several years, there is the tendency that the conception of double-layered photoconductive structures is positively taken in consideration. Above all, a main conception which has now been investigated is that a carrier generation layer and a carrier transport layer in which positive holes are mobile are laminated in this order, and in general, the surface of the carrier transport layer is negatively charged with electricity.
As described above, the separation of the functions permits to independently develop materials having the functions of the generation of the carrier and materials having the function of the transport of the carrier, and as a result, many carrier generation materials and carrier transport materials having various molecular structures have been developed.
According to the classification of the carrier transport materials from structural characteristics, these typical examples already developed include hydrazone compounds Japanese Patent Application Laid-open No. (Sho) 54-59143!, stilbene-styryl compounds Japanese Patent Application Laid-open No. (Sho) 58-198043!, triarylamine compounds Japanese Patent Publication No. (Sho) 58-32372!, phenothiazine compounds, triazole compounds, quinoxaline compounds, oxadiazole compounds, oxazole compounds, pyrazoline compounds, triphenylmethane compounds, dihydronicotinamide compounds, indoline compounds and semicarbazone compounds.
As mentioned above, however, as the carrier transport materials, many organic compounds have been developed, but there has been no organic compound which can solve all of the problems of:
In consequence, there has not been obtained any material which can meet the above-mentioned fundamental characteristics required as the photoreceptor, further mechanical strength, durability and the like.